Input Device

1. An input device for inputting information corresponding to a change in a pressure due to a load applied thereto, the input device comprising: a first piezoelectric sensor and a second piezoelectric sensor that generate a respective charge corresponding to the change in the pressure due to the load; a first charge detection circuit configured to output a first detection signal based on the charge generated in the first piezoelectric sensor and the charge generated in the second piezoelectric sensor which are received at an input node of the first charge detection circuit; from the first piezoelectric sensor and the second piezoelectric sensor to the first charge detection circuit, the switch circuit forming a first path during a first time period and a second path during a second time period, the first time period and the second time period being alternately repeated; and a surface member having a surface for receiving the load, the surface member covering at least a part of the first piezoelectric sensor and the second piezoelectric sensor, wherein the first piezoelectric sensor includes: a first piezoelectric member; a first negative electrode provided to the first piezoelectric member at a portion where a negative charge is generated when the pressure changes in a predetermined direction; and a first positive electrode provided to the first piezoelectric member at a portion where a positive charge is generated when the pressure changes in the predetermined direction, the first positive electrode being disposed closer to the surface than the first negative electrode; wherein the second piezoelectric sensor includes: a second piezoelectric member; a second positive electrode provided to the second piezoelectric member at a portion where a positive charge is generated when the pressure changes in the predetermined direction; and a second negative electrode provided to the second piezoelectric member at a portion where a negative charge is generated when the pressure changes in the predetermined direction, the second negative electrode being disposed closer to the surface than the second positive electrode; wherein the first path transmits a first charge from the first positive electrode to the first charge detection circuit during the first time period, and the second path transmits a second charge from the second negative electrode to the first charge detection circuit during the second time period, and wherein the first charge detection circuit accumulates the first charge during the first time period, accumulates the second charge during the second time period, and combines the first and second charges by reversing a sign of one of the first charge and the second charge to produce a combined charge, thereby outputting the first detection signal corresponding to the combined charge.

2. The input device according to claim 1 , wherein: the first charge detection circuit is further configured to bring a voltage of the charge received at the input node to a reference voltage; the switch circuit connects the first positive electrode to the input node during the first time period and connects the second negative electrode to the input node during the second time period; and the reference voltage is applied to the first negative electrode and the second positive electrode.

3. The input device according to claim 2 , wherein the switch circuit connects the first negative electrode to the reference voltage during the first time period and connects the second positive electrode to the reference voltage during the second time period.

4. The input device according to claim 1 , wherein: the first negative electrode and the second positive electrode are electrically connected to each other; the first charge detection circuit is further configured to bring a voltage of the charge received at the input node to a reference voltage; and the switch circuit connects the first positive electrode to the input node and connects the second negative electrode to the reference voltage during the first time period, and the switch circuit connects the second negative electrode to the input node and connects the first positive electrode to the reference voltage during the second time period.

5. The input device according to claim 2 , wherein the first charge detection circuit includes: a feedback capacitor having a first end and a second end, the first end being connected to the input node; an operational amplifier configured to output an output voltage from an output terminal thereof to the second end of the feedback capacitor, the output voltage being obtained by amplifying a difference between the voltage at the input node and the reference voltage; and a connection switching circuit configured to alter a direction of connection of the feedback capacitor between the output terminal and the input node by the first time period and the second time period.

6. The input device according to claim 1 , the input device further comprising: a detection electrode and a drive electrode configured to form a capacitor therebetween, an electrostatic capacitance of the capacitor changing in response to proximity of an object that applies the load to the input device; a drive circuit configured to apply a periodic drive voltage to the drive electrode, the periodic drive voltage having one of a rising edge and a falling edge in the first time period and the other of the rising edge and the falling edge in the second time period; and a second charge detection circuit configured to output a second detection signal based on a charge received from the capacitor via the detection electrode in response to a change in the drive voltage applied to the drive electrode, wherein the second charge detection circuit accumulates the charge from the capacitor during the first time period as a third charge, accumulates the charge from the capacitor during the second time period as a fourth charge, and combines the third and fourth charges by reversing a sign of one of the third charge and the fourth charge to produce a second combined charge, thereby outputting the second detection signal corresponding to the second combined charge; and wherein the switch circuit switches the first path and the second path in accordance with the drive voltage.

7. The input device according to claim 6 , wherein the drive electrode is disposed closer to the surface than the detection electrode, and the first piezoelectric sensor and the second piezoelectric sensor are disposed closer to the surface than the drive electrode such that at least a part of the first piezoelectric sensor and the second piezoelectric sensor overlaps the drive electrode in a plan view viewed from a direction facing the surface.

8. The input device according to claim 6 , wherein the second charge detection circuit includes: a feedback capacitor having a first end and a second end, the first end being connected to the detection electrode; an operational amplifier configured to output an output voltage from an output terminal thereof to the second end of the feedback capacitor, the output voltage being obtained by amplifying a difference between a voltage at the detection electrode and the reference voltage; and a connection switching circuit configured to switch a direction of connection of the feedback capacitor between the output terminal and the detection electrode.

9. An input device for inputting information corresponding to a change in a pressure due to a load applied thereto, the input device comprising: a piezoelectric sensor that generates a charge corresponding to the change in the pressure due to the load; a first charge detection circuit configured to output a first detection signal based on the charge generated in the piezoelectric sensor; and a switch circuit configured to form a path for transmitting the charge from the piezoelectric sensor to the first charge detection circuit, the switch circuit forming a first path during a first time period and forming a second path during a second time period, the first time period and second time period being alternately repeated; wherein the piezoelectric sensor includes a piezoelectric member, a positive electrode provided to the piezoelectric member at a portion where a positive charge is generated when the pressure changes in a predetermined direction, and a negative electrode provided to the piezoelectric member at a portion where a negative charge is generated when the pressure changes in the predetermined direction, wherein the first path transmits a first charge from the positive electrode to the first charge detection circuit during the first time period, and the second path transmits a second charge from the negative electrode to the first charge detection circuit during the second time period, and wherein the first charge detection circuit accumulates the first charge during the first time period, accumulates the second charge during the second time, and combines the first and second charges by reversing a sign of one of the first charge and the second charge to produce a combined charge, thereby outputting the first detection signal corresponding to the combined charge.

10. An input device for inputting information corresponding to a change in a pressure due to a load applied thereto, the input device comprising: a piezoelectric sensor that generates a charge corresponding to the change in the pressure; a first charge detection circuit configured to output a first detection signal based on the charge generated in the piezoelectric sensor and input to the first charge detection circuit; a detection electrode and a drive electrode configured to form a capacitor therebetween, an electrostatic capacitance of the capacitor changing in response to proximity of an object that applies the load to the input device; a drive circuit configured to apply a periodic drive voltage to the drive electrode; a second charge detection circuit configured to output a second detection signal based on a charge input thereto from the detection electrode, the charge being accumulated in the capacitor in response to a change in the drive voltage; and a surface member that has a surface for receiving the load and that covers at least a part of the piezoelectric sensor, the detection electrode, and the drive electrode, wherein the drive electrode is disposed closer to the surface than the detection electrode, and the piezoelectric sensor is disposed closer to the surface than the drive electrode such that at least a part of the piezoelectric sensor overlaps the drive electrode in a plan view viewed from a direction facing the surface.

11. The input device according to claim 1 , wherein the first charge detection circuit accumulates the first charge and the second charge for a plurality of repetitions of the first time period and the second time period, respectively, before combining into the combined charge.

12. The input device according to claim 9 , wherein the first charge detection circuit accumulates the first charge and the second charge for a plurality of repetitions of the first time period and the second time period, respectively, before combining into the combined charge.